US8593922B2 - Optical disc apparatus, focus control method and control program - Google Patents

Optical disc apparatus, focus control method and control program Download PDF

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US8593922B2
US8593922B2 US13/243,157 US201113243157A US8593922B2 US 8593922 B2 US8593922 B2 US 8593922B2 US 201113243157 A US201113243157 A US 201113243157A US 8593922 B2 US8593922 B2 US 8593922B2
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optical disc
layer
focus
data
maximum level
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US20120075973A1 (en
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Kaoru KOSAKA
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JVCKenwood Corp
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J&K Car Electronics Corp
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0945—Methods for initialising servos, start-up sequences
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/02—Control of operating function, e.g. switching from recording to reproducing
    • G11B19/12—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/094—Methods and circuits for servo offset compensation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
    • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete layers

Definitions

  • the present invention relates to an optical disc apparatus, a focus control method, and a control program capable of high-quality reproduction of an optical disc having at least two data layers.
  • Optical discs for which a laser beam is used in recording/reproduction have been in wide use as a storage medium for audio data, video data, and other several types of digital data.
  • Representative of optical discs are CD (Compact Disc), DVD (Digital Versatile Disc), BD (Blu-ray Disc), etc.
  • representative of data-writable optical discs are CD-R, CD-RW, DVD-R, DVD-RW, BD-RE, etc.
  • a representative of such optical disc is DVD-DL (Digital Versatile Disc Dual Layer) having two data layers on one side.
  • a laser beam is directed onto the optical disc while the focal point is being shifted from the surface side (a laser side) to the far side of the optical disc.
  • the shift of focal point is perform to acquire a characteristic curve of a FE (Focus Error) signal (a focus-error signal curve, referred to as a FES curve, hereinafter) of the optical disc, for discriminating the type of the disc, obtaining the in-focus point, etc.
  • FE Focus-error signal curve
  • FIG. 1 shows a FES curve for a regular single-sided dual-layer DVD having data layers separated from each other with an enough distance.
  • FES curve portions there are two FES curve portions.
  • One FES curve portion corresponds to a layer L 0 that is a first data layer on the surface side.
  • the other FES curve portion corresponds to a layer L 1 that is a second data layer on the far side.
  • the FES curve portions are connected to form a FES curve.
  • several types of control such as focus control, can be performed with regular procedures.
  • U.S. Pat. No. 6,392,965 discloses an invention related to an optical pickup device for achieving accurate focus control of an optical disc with close data layers by having main photoreceptive domains and auxiliary photoreceptive domains for mitigating the effect of reflected beams from the close data layers.
  • a purpose of the present invention is to provide an optical disc apparatus, a focus control method, and a control program capable of high-quality reproduction of an optical disc having close data layers even with a low-priced pickup device.
  • the present invention provides an optical disc apparatus comprising: an optical pickup device configured to detect a value of a return beam reflected by an optical disc and to output the detected value; a controller configured to focus control based on the detected value; and a discriminator configured, when the optical disc has at least a first data layer and a second data layer on which data is recorded or from which data is reproduced, the first data layer being located closer than the second data layer to a beam-incident surface of the optical disc, to obtain a maximum level in a positive side and a maximum level in a negative side on a characteristic curve of a focus error signal obtained from the optical disc, for both of the first and second data layers, to obtain a first focus balance value based on the maximum levels in the positive and negative sides for the first data layer and a second focus balance value based on the maximum levels in the positive and negative sides for the second data layer, and to determine whether a difference between the first and second focus balance values satisfies at least either a first requirement or a second requirement, the first requirement requiring that
  • the present invention provides a focus control method for an optical disc having at least a first data layer and a second data layer on which data is recorded or from which data is reproduced, the first data layer being located closer than the second data layer to a beam-incident surface of the optical disc, the method comprising the steps of: obtaining a maximum level in a positive side and a maximum level in a negative side on a characteristic curve of a focus error signal obtained from the optical disc, for both of the first and second data layers; obtaining a first focus balance value based on the maximum levels in the positive and negative sides for the first data layer and a second focus balance value based on the maximum levels in the positive and negative sides for the second data layer; determining whether a difference between the first and second focus balance values satisfies at least either a first requirement or a second requirement, the first requirement requiring that the difference exceed a predetermined threshold value and the second requirement requiring that the second focus balance value be smaller than a predetermined threshold value; and selecting a focus balance value depending on a
  • the present invention provides a control program running on a computer for focus control of an optical disc having at least a first data layer and a second data layer on which data is recorded or from which data is reproduced, the first data layer being located closer than the second data layer to a beam-incident surface of the optical disc, the program comprising: a program code of obtaining a maximum level in a positive side and a maximum level in a negative side on a characteristic curve of a focus error signal obtained from the optical disc, for both of the first and second data layers; a program code of obtaining a first focus balance value based on the maximum levels in the positive and negative sides for the first data layer and a second focus balance value based on the maximum levels in the positive and negative sides for the second data layer; a program code of determining whether a difference between the first and second focus balance values satisfies at least either a first requirement or a second requirement, the first requirement requiring that the difference exceed a predetermined threshold value and the second requirement requiring that the second focus balance value be smaller than
  • FIG. 1 shows a FES curve for a regular dual-layer DVD
  • FIG. 2 is a block diagram schematically showing the configuration of an optical disc apparatus according to the present invention.
  • FIG. 3 is a flow chart explaining an operation of an optical disc apparatus, a focus control method, and a control program according to the present invention
  • FIG. 4 is a view showing examples of FES curves for a dual-layer optical disc D having close data layers
  • FIG. 5 is a graph showing the relationship between a focus balance value and a digital jitter for a dual-layer optical disc having close data layers.
  • FIG. 6 is view showing time charts of a FE signal in (a) and a focus drive signal in (b) for a dual-layer DVD having distant data layers.
  • FIG. 2 is a block diagram schematically showing the configuration of the optical disc apparatus 60 . No detailed explanation is given to the elements of FIG. 2 , such as an A/D converter, which are not directly related to the present invention.
  • the optical disc apparatus 60 is equipped with a turntable 63 to detachably clamp an optical disc D placed thereon.
  • the turntable 63 is fixed to the rotation shaft of a spindle motor 62 .
  • the spindle motor 62 rotates at a specific rotating speed with an instruction from a controller 61 via a spindle-motor driver 65 .
  • the optical disc D placed on the turntable 63 also rotates at the specific rotating speed.
  • optical pickup device 70 Provided under the optical disc D is an optical pickup device 70 connected to a sled motor 67 .
  • the controller 61 controls the rotation of the sled motor 67 so that the optical pickup device 70 moves in the radius direction of the optical disc D.
  • the optical pickup device 70 is equipped with a laser source 72 suitable for the optical disc D.
  • the optical pickup device 70 may be equipped with several laser sources 72 for several types of optical discs D.
  • the controller 61 sends a drive instruction to the laser source 72 via a laser driver 84 so that the laser source 72 emits a laser beam having a specific wavelength.
  • the emitted laser beam is converted into parallel beams via a collimator lens 73 .
  • the parallel beams pass through a beam splitter 75 and are then converted into circularly polarized beams by a ⁇ /4 plate 76 .
  • the circularly polarized beams are converged and irradiated onto a data layer of the optical disc D via an objective lens 78 .
  • the irradiated laser beam is reflected by the data layer and reaches the beam splitter 75 as a return beam via the objective lens 78 and the ⁇ /4 plate 76 .
  • the return beam is then reflected by the beam splitter 75 and enters a multi-segment photodetector 83 via a detection lens 81 and a cylindrical lens 82 .
  • the multi-segment photodetector 83 has a plurality of photoreceptive regions for detecting a return beam. A detected value output by the multi-segment photodetector 83 is output to a TE (tracking error)-signal detector 86 for tracking control, a FE-signal detector 90 for focus control, and a RF-signal processor 96 .
  • TE tilt error
  • the TE-signal detector 86 performs specific computation to the detected value of the multi-segment photodetector 83 based on known DPD (Differential Phase Detection) to output a tracking error signal TE that is output to the controller 61 via an A/D converter.
  • DPD Different Phase Detection
  • the controller 61 generates a tracking-control drive signal TD based on the tracking error signal TE and outputs the drive signal TD to a tracking (TD) driver 89 via a D/A converter.
  • the TD driver 89 controls a tracking coil 79 based on the tracking-control drive signal TD so that the objective lens 78 moves for tracking control of the optical disc D.
  • the FE-signal detector 90 receives the output signal of the multi-segment photodetector 83 and performs specific computation based on known astigmatic focus-error detection to output a focus error signal FE to the controller 61 via an A/D converter.
  • the controller 61 generates a focus-control drive signal FD based on the focus error signal FE that is output to a focus (FD) driver 93 via a D/A converter.
  • the FD driver 93 controls a focus coil 80 based on the focus-control drive signal FD so that the objective lens 78 moves (a focusing operation) for focus control of the optical disc D.
  • the focus control requires focus balance values obtained based on a FES curve for high reproduction quality.
  • a previously set focus balance value is used for the second data layer L 1 at the far side.
  • the focus balance value is known from U.S. Patent Publication No. 2008/0298181.
  • the RF-signal processor 96 receives the output signal of the multi-segment photodetector 83 to obtain a main-data signal RF (a RF signal) stored in the data layer of the optical disc D with known processing.
  • the main-data signal RF is output to a reproduction apparatus (not shown) and output therefrom as a video or audio signal.
  • the controller 61 is provided with a discriminator 61 a for distinguishing the type of the optical disc D set on the turntable 63 and a memory 61 b for storing focus balance values and other values to be used when the optical disc D has close data layers.
  • the discriminator 61 a and the memory 61 b may be provided separately from the controller 61 .
  • the structure and type of the optical disc D are defined as follows in the present invention.
  • the optical disc D has at least two layers L 0 and L 1 on which data is recorded or from which data is reproduced.
  • the layer L 0 is a first data layer located closer to a beam-incident surface of the optical disc D.
  • the layer L 1 is a second data layer located distant from the beam-incident surface of the optical disc D. That is, the first data layer is located closer than the second data layer to the beam-incident surface of the optical disc D.
  • the optical disc D is categorized into two types.
  • a first type is a regular dual-layer optical disc (or DVD) having at least two data layers, the distance between the data layers being almost the center of a standard range.
  • a second type is a dual-layer optical disc (or DVD) having at least two data layers, the distance between the data layers being smaller than the first type.
  • the first type is referred to as a regular dual-layer DVD having distant data layers, hereinafter.
  • the second type is referred to as a dual-layer DVD having close data layers, hereinafter.
  • the discriminator discriminates between the regular dual-layer DVD having distant data layers and the dual-layer DVD having close data layers. And, when the optical disc D is determined as the dual-layer DVD having close data layers, focus balance values and other values are retrieved from the memory 61 b for several types of control of the optical disc D having close data layers.
  • the known DPD is used for tracking control.
  • Another known technique that can be used in the embodiment is DPP ((Differential Push Pull) with return beams.
  • DPP (Differential Push Pull) with return beams.
  • a laser beam is separated into a main beam and two sub-beams, and the two sub-beams are used as the return beams.
  • the control program in this embodiment corresponds to the controller 61 and the discriminator 61 a of FIG. 2 , that are configured with a computer. Moreover, although the explanation is made with a dual-layer DVD, it is applicable to any type pf optical disc having a plurality of data layers.
  • an optical disc D is placed on the turntable 63 of the optical disc apparatus 60 according to a specific procedure, which initiates a start-up process to the optical disc D (step S 100 ).
  • the controller 61 performs a control procedure to rotate the optical disc D and emit a laser beam onto the optical disc D to determine the type of the optical disc with a known optical-disc discrimination procedure (step S 102 ).
  • step S 200 If the optical disc D is determined as any type except for a dual-layer DVD (NO in step S 102 ), the succeeding steps for the determined type are performed (step S 200 ).
  • the discriminator 61 a of the controller 61 obtains a FES curve for the optical disc D (step S 104 ). If a FES curve has already been obtained through the optical-disc discrimination procedure in step S 102 , this FES curve is used.
  • FIG. 4 Shown in (a) and (b) of FIG. 4 are examples of FES curves for dual-layer optical DVDs having closer data layers than regular optical discs available on the market.
  • Regular optical discs have data layers with an average distance therebetween that are dual-layer optical DVDs having distant data layers, according to the definition in the present invention.
  • FES curves for dual-layer DVDs having close data layers have curve portions of different levels between the layer L 0 (the first data layer) and the layer L 1 (the second data layer).
  • the layer L 1 exhibits a low level in the positive side.
  • the layer L 0 exhibits a low level in the negative side and the layer L 1 exhibits a low level in the positive side.
  • the discriminator 61 a discriminates between a dual-layer DVD having close data layers and that having distant data layers for the optical disc D placed on the turntable 63 .
  • the discriminator 61 a obtains several levels of the FES curve (step S 106 ), as follows: the maximum level FEL 0 (+) in the positive side and the maximum FEL 0 ( ⁇ ) in the negative side for the layer L 0 and the maximum level FEL 1 (+) in the positive side and the maximum FEL 1 ( ⁇ ) in the negative side for the layer L 1 .
  • the discriminator 61 a determines whether the obtained levels satisfy at least either a first or a second requirement which will be explained later (step S 108 ).
  • the optical disc D is determined as a dual-layer DVD having close data layers if either the first or second requirement is satisfied or both requirements are satisfied. Moreover, it is more preferable to add a third requirement which will also be explained later for more accurate determination of disc type. In this case, the optical disc D is determined as a dual-layer DVD having close data layers if the first and third requirements, the second and third requirements, or the first, second and third requirements are satisfied.
  • Curve balance values SBAL(L 0 ) and SBAL(L 1 ) for the layers L 0 and L 1 , respectively, are calculated as follows.
  • SBAL ( L 0) ( FEL 0(+) ⁇ FEL 0( ⁇ ))/( FEL 0(+)+ FEL 0( ⁇ )) ⁇ 100(%)
  • SBAL ( L 1) ( FEL 1(+) ⁇ FEL 1( ⁇ ))/( FEL 1(+)+ FEL 1( ⁇ )) ⁇ 100(%)
  • the optical disc D is determined as a dual-layer DVD having close data layers. This is the first requirement.
  • the threshold value A is preferably in the range from 30% to 40%. In this range, 32% is the most recommended value for the threshold value A.
  • the first requirement is provided for a dual-layer DVD having close data layers that exhibits a big difference between the curve balance values SBAL(L 0 ) and SBAL(L 1 ).
  • threshold value A is just an example and are decided according to the actual distance between the layers L 0 and L 1 of a dual-layer DVD. This is also true for threshold values B and C which will be explained later.
  • the optical disc D is determined as a dual-layer DVD having close data layers.
  • the threshold value B is preferably in the range from ⁇ 20% to ⁇ 30%. In this range, ⁇ 23% is the most recommended value for the threshold value B.
  • the second requirement is provided for a dual-layer DVD having close data layers that exhibits a large curve balance value SBAL(L 1 ) in the negative side, especially, for the layer L 1 .
  • the optical disc D is determined as a dual-layer DVD having close data layers.
  • the threshold value C is preferably in the range from 200% to 300%. In this range, 250% is the most recommended value for the threshold value C.
  • the third requirement is provided for a dual-layer DVD having close data layers that exhibits a low level of FEL 1 (+), hence the ratio of FEL 0 (+) to FEL 1 (+) becomes very high.
  • optical discs D available on the market, that exhibit higher reflectance on the layer L 0 than on the layer L 1 .
  • this type of optical disc D satisfies the third requirement irrespective of the distance between the layers L 0 and L 1 . Therefore, it is preferable that the third requirement is combined with either the first or second embodiment, or with both requirements for determining the type of optical discs D.
  • step S 110 the operating mode is switched to a special mode (step S 110 ), followed by the succeeding steps S 112 including focus control in reproduction of the optical disc D in the special mode.
  • step S 108 if it is determined in step S 108 that the optical disc D is not the type having close data layers, the process moves to step S 204 for the succeeding steps for a regular dual-layer DVD.
  • the controller 61 uses a focus balance value previously stored in its memory 61 b for the focus control of the layer L 1 in the far side.
  • the controller 61 uses a focus balance value stored in the memory 61 b .
  • the controller 61 uses a focus balance value obtain by a known technique.
  • a dual-layer DVD having close data layers that exhibits a FES curve such as shown in (a) of FIG. 4 , exhibits a very low level of FEL 1 (+) at the layer L 1 .
  • FES curve such as shown in (a) of FIG. 4
  • FEL 1 (+) at the layer L 1 exhibits a very low level of FEL 1 (+) at the layer L 1 .
  • FIG. 5 shows the relationship between the focus balance value and digital jitter for the layer L 1 .
  • the digital jitter indicates the reproduction quality of RF signals with numerical values, relating to jitters. A larger digital jitter value indicates higher reproduction quality.
  • a solid-line curve in FIG. 5 shows the change in digital jitter for the layer L 1 of a dual-layer DVD having close data layers.
  • a broken-line curve in FIG. 5 shows the change in digital jitter for the layer L 1 of a dual-layer DVD having distant data layers.
  • a dual-layer DVD having distant data layers exhibits a moderate decrease in digital jitter to the change in focus balance value. Especially, at a focus balance closer to zero, the digital jitter is roughly constant.
  • the broken-line curve in FIG. 5 teaches that it is possible to reproduce data from the layer L 1 of a dual-layer DVD having distant data layers, without defocus adjustments.
  • a dual-layer DVD having close data layers exhibits a steep decrease in digital jitter to the change in focus balance value.
  • the digital jitter is very small so that data may not be reproduced.
  • a previously stored appropriate focus balance value is used in accessing the layer L 1 of a dual-layer DVD having close data layers, as described above. Therefore, the present invention achieves high reproduction quality at the layer L 1 of a dual-layer DVD having close data layers.
  • a focus balance value for the layer L 1 in the special mode is obtained with actual measurements. For example, when the solid-line curve shown in FIG. 5 is obtained with actual measurements, a focus balance value (for example, 26) that gives almost a peak jitter is used for reproduction of the layer L 1 of a dual-layer DVD having close data layers.
  • the focus balance value used in the special mode depends on the optical pickup device 70 , a micro computer of the controller 61 , and other parts of the optical disc apparatus 60 . It is therefore preferable to make actual measurements to obtain a focus balance value used in the special mode for each optical disc apparatus 60 if the configuration is modified.
  • an appropriate focus balance value can be obtained with the determination of disc type according to the first, second, and third requirements described above.
  • an acceleration pulse of the focus drive signal is turned on to rapidly shift the in-focal point towards the layer L 1 on the far side, with the change in FE-signal level in accordance with a FES curve.
  • the acceleration pulse is turned off so that the movement of the in-focal point is decelerated.
  • a break pulse of the focus drive signal is turned on to further decelerate the movement of the in-focal point.
  • the break pulse is turned off so that the in-focal point of the laser beam moves to an in-focal point L 1 Fp on the layer L 1 and stops thereat.
  • a dual-layer DVD having close data layers exhibits a low maximum level FEL 0 ( ⁇ ) in the negative side for the layer L 0 or a low maximum level FEL 1 (+) in the positive side for the layer L 1 .
  • These levels may be lower than or close to the threshold level Vape, Vbps, or Vbpe shown in (a) of FIG. 6 , depending on a dual-layer DVD having close data layers.
  • Vape threshold level
  • Vbps Vbpe shown in (a) of FIG. 6
  • the times t 1 , t 2 , and t 3 shown in (b) of FIG. 6 can be adjusted to set a specific focus drive-signal pattern for focus jump at a constant focal-point movement speed.
  • threshold levels Vape, Vbps, and Vbpe shown in (a) of FIG. 6 used for control of acceleration and brake pulses can be adjusted to set a specific focus drive-signal pattern for focus jump, depending on the optical disc D that is determined as a dual-layer DVD having close or distant data layers.
  • An appropriate focus drive-signal pattern depends on the characteristics of the optical pickup device 70 and other factors. Therefore, it is preferable to set an appropriate focus drive-signal pattern for each type of optical disc, which can be done with measurements of a FES curve, focus jump by a manual operation, etc.
  • an optical disc is distinguished between a dual-layer DVD having close data layers and that having distant data layers, by using a FES curve.
  • the optical disc is determined as a dual-layer DVD having close data layers, a previously set appropriate focus balance value is used for focus control so that high reproduction quality is achieved, with no necessity of a special optical pickup device or other special circuitry, according to the present invention.
  • the optical disc is determined as a dual-layer DVD having close data layers, accurate focus jump can be performed with an appropriate focus drive-signal pattern, according to the present invention.
  • a program running on a computer to achieve the function of the controller 61 (and the discriminator 61 a when provided separately from the controller 61 ) is embodied in the present invention.
  • Such a program may be retrieved from a storage medium or transferred over a network and installed in a computer.

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